Peripheral Component Interconnect Express (PCIe) is a high speed bus interface, which can connect a host system processor unit with integrated peripherals, such as solid state drives (SSD). The features and specifications of the PCIe bus interface are described, for example, in “PCI Express Base Specification,” revision 3.0, Nov. 10, 2010, and in an Engineering Change Notice (ECN) of the PCI Special Interest Group (SIG), entitled “L1 PM Substates with CLKREQ,” Aug. 23, 2012, which are incorporated herein by reference.